1. Field of the Invention (Technical Field)
This invention relates to making temporary electrical contact to devices or circuits under test.
2. Description of Related Art
Testing of electronic devices and circuits prior to final packaging is an important aspect of integrated circuit fabrication, and has been significant for some time. Accordingly, methods of making temporary electrical contact for such testing have been thoroughly investigated. It is helpful to classify probes for making temporary electrical contact as being either horizontal probes or vertical probes. Horizontal probes are substantially parallel to the chip plane. For example, a horizontal probe array can be arranged as a set of horizontal needles extending inward from a frame to make contact to pads at the periphery of an IC chip.
In contrast, vertical probes are substantially perpendicular to the chip plane. For example, in FIG. 1a, vertical probe 102 is shown having tip 120 making contact with contact pad 130, where contact pad 130 is shown in side view. Frequently, as shown here, vertical probes include a curved section. One purpose of the curved section of a vertical probe is to help determine the exact nature of scrub motion tip 120 makes with respect to contact pad 130 when contact is made. The ability to fine-tune such scrub motion by appropriate probe design is a significant advantage of vertical probe relative to horizontal probes. Arrays of vertical probes, such as 104 on FIG. 1b, are also known in the art. This figure illustrates another advantage of vertical probes relative to horizontal probes, namely that arrays of vertical probes can often be more closely packed than similar arrays of horizontal probes, particularly for 2-D probe arrays.
Vertical probes are referred to as guided probes if they probe assembly includes one or more guide plates having slots through which the probes pass to control probe motion. In some cases, no guide plates are employed, and the resulting vertical probes are referred to as “free” (i.e., un-guided) vertical probes. U.S. Pat. No. 5,923,178 is a representative prior art example of free vertical probes. U.S. Pat. No. 4,901,013, U.S. Pat. No. 5,952,843, and U.S. Pat. No. 5,945,836 are representative examples of prior art guided vertical probe approaches.
As electronic circuit technology progresses, contact pads tend to become smaller and more closely spaced, which places increasingly severe demands on probe technology. For example, probing of contact pads spaced by 80 μm or less is presently of increasing interest in manufacturing. As described in greater detail below, conventional vertical probe approaches tend to fail for such small pitches.
Accordingly, it would be an advance in the art to provide vertical probing of contact pads having a pitch of 80 μm or less.